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8 Thus, a thin overlay should not be considered a preventive traffic loads, and the interaction between the two. However, maintenance treatment when it is applied to badly alligator- initial deterioration results almost solely from environmental cracked pavement, neither should a slurry seal when it is effects. placed on a cracked and oxidized surface. Selecting the appro- It is a fundamental tenet of treatment performance that the priate treatment together with determining the appropriate tim- same treatment performs differently when applied at differ- ing of its placement constitutes a preventive maintenance strat- ent times in the life of the pavement (or on pavements in egy. These elements of preventive maintenance are captured varying condition). For example, placing a thin bituminous in the following definition (1): surfacing (such as a chip seal) on top of a 2-month old pave- ment may not increase the pavement's life because the pave- . . . the planned strategy of cost effective treatments to an ment may show structural deterioration once the surfacing existing roadway system and its appurtenances that pre- wears off. Similarly, placing the same treatment near the end serves the system, retards future deterioration, and main- of the pavement's life (i.e., when the surface is aged and tains or improves the functional condition of the system worn and the pavement is exhibiting signs of structural dete- [without increasing structural capacity]. rioration) will have a minimal effect on pavement perfor- mance because the condition of the underlying pavement will Many factors should be considered when selecting the control performance. Therefore, for a given pavement, there most appropriate preventive maintenance treatment for a given is an optimal age or condition (or a range of age or condition) pavement. Some of those factors relate to the limitations of the where the benefit/cost (B/C) ratio associated with a chosen treatments; important attributes or characteristics of some of treatment is maximized; this is defined as the optimal timing the common preventive maintenance treatments are described for the treatment. later in this chapter. Constructibility and customer satisfac- tion are other factors to consider. Constructibility pertains to the availability of skilled contractors and suitable materials, PREVENTIVE MAINTENANCE environmental constraints, and other factors such as traffic TREATMENTS FOR BITUMINOUS- AND control constraints and available lane closures that affect the CONCRETE-SURFACED PAVEMENTS placement of the treatments. Customer satisfaction pertains Different approaches are used to identify which pavement to traffic disruption, noise impacts, surface friction, and ride treatments are considered "preventive." For example, the quality; it is becoming increasingly important for many agen- Michigan DOT (MDOT) preventive maintenance program cies. While all these issues are important, this project focuses lists the 20 treatments shown in Table 1 (11). In Caltrans' on performance attributes. These attributes include the treat- Capital Preventive Maintenance (CAPM) program, grinding ment's expected life, the effect of the existing pavement con- and removal and replacement of failed slabs are described for dition on performance of the treatment, the effect of the treat- concrete-surfaced pavements, and thin overlays and "pre- ment on the pavement condition, the effect of the climate on mium seal coats" (microsurfacing, polymer- and rubber- treatment performance, and the treatment cost. modified chip seals, modified binder open-graded hot-mix asphalt (HMA) blankets, and thin, hot-applied, gap-graded Pavement Deterioration and Treatment Timing applications) are described for bituminous-surfaced pavements (12). In an FHWA course on pavement preservation, at least Deterioration of a well designed and constructed pave- 11 bituminous-surfaced pavement treatments and 8 concrete- ment occurs as a result of the effects of the environment, the surfaced pavement treatments are described (13). TABLE 1 Treatments included in MDOT's 1999 and 2000 Capital Preventive Maintenance program (11) Concrete-Surfaced Pavements Bituminous-Surfaced Pavements Full depth concrete pavement repair Bituminous overlay Joint resealing Surface milling and bituminous overlay Crack sealing Ultrathin bituminous overlay Joint and surface spall repair Crack treatment Dowel bar retrofit Overband crack filling Diamond grinding Microsurfacing Underdrain outlet repair and cleaning Chip seals Concrete pavement restoration Bituminous shoulder ribbons Bituminous shoulder ribbons Shoulder seals Paver placed surface seals Hot in-place bituminous recycling